Opinions and beliefs are very similar. Because of this, some people don't understand the difference between an opinion and a belief. When you have an opinion about something, you feel a certain way about something. When you believe something, you think that something exists or a state exists. Knowing the difference is important because when people treat beliefs like opinions people tend to do two things. The first is that they discard the consequences of the possibility that the belief is right.
The second is that they overlook possible solutions that can be found by addressing the beliefs underlying an opinion. If I say that I like Linux, it is an opinion. If I say that despite the fact that I like Linux, Microsoft Windows is currently the better operating system for desktops, that is a belief. People can try Linux and Windows for themselves and if they can do the things they want to do easier in Linux than Windows then Linux is the better operating system.
"Linux is the better operating system," says something about the operating system. "I like Windows," says something about me. Statements of beliefs similar to "You'd be better off if you stopped smoking," are often dismissed as opinions, when it is a belief that if examined by the person to whom the statement is directed, may help them that person have a healthier life. Life is hard enough without people making it harder on themselves by failing to examine their own and other people's beliefs. When a person fails to examine their own beliefs, they make mistakes when those beliefs aren't true.
When a person fails to examine the beliefs of another, they lose an opportunity for both theirs and the other person's beliefs to be corrected, so that both of them are kept from making mistakes.